Preparation of the concrete has for some time been done in fully-equipped facilities which load the components of the mixture into containers equipped on mobile concrete mixers, which generally perform the mixing during transport of the concrete to the places of destination. Once the concrete has been unloaded, the concrete mixer truck returns to the facility of origin, which the container in which the concrete has been mixed is internally washed using water and is emptied of the residues of the concrete, so that it is ready to perform a further transport operation. The fluid extracted from the container, which is in substance a very water-diluted concrete, is placed in special devices which wash and separate the aggregates in order for them to be re-used; the liquid part, containing cement and additives used for concrete in suspension, is generally freed from the additives and re-utilised for new mixtures, or is completely purified and sent off to the drains for disposal.
Washing devices are known which comprise an inclined screw conveyor in which, through a loading mouth, the fluid is introduced. The propeller is generally constituted by a metal spiral supported by a central shaft. The aggregate substances, which are heavier, are deposited on the bottom of the screw conveyor and are transported by the motorised propeller towards a discharge mouth. The liquid, which partially fills the screw conveyor such as to wash the aggregate substances during transport thereof, exits by skimming from the device and is sent on to further following operations.
It frequently occurs that when the device is at rest, for example during the night-time, weekends or holidays, material is left internally of the device. The material tends to solidify and produce encrustations on the internal walls and the propeller of the screw. On restart of work these encrustations have to be broken up so that the device can recommence its normal functioning.
For this reason these devices must have very robust structures, and thus are heavy and expensive to build; they also consume rather large amounts of energy and are therefore expensive to run. Notwithstanding this, it sometimes happens that external means are required, such as for example a pneumatic jack-hammer, to break up the encrustations and prevent breakage of parts of the device.
The aim of the present invention is to eliminate the above-described drawbacks, by providing a device having a structure which is lighter and less expensive than in known devices, and which offers no difficulties in breaking up the solidified parts which might have formed internally of the device.
An advantage of the invention is that it consumes limited amounts of power in comparison with prior-art devices.
A further advantage of the invention is that it makes cleaning and maintaining the device simple.